The present invention relates to new soluble phenylated polyimides, their use as coatings, solution castable films, gas or molecular separation membranes, high modulus, high tensile strength fibers, and as molecular composite reinforcing agents and a process for the manufacturing of 3,6-diarylpyromellitic dianhydride.
Polyimides are condensation polymers having the following repeat unit formula (I) below: ##STR1## where L is a tetravalent organic radical and Q is a divalent organic radical. L can either be a simple tetra substituted benzene radical or a tetra substituted polynuclear aromatic radical. Q is normally an aromatic radical.
Polyimides are used in industry as binders for advanced composite materials especially in aerospace industries. Polyimides are also useful as components which require excellent thermal, electrical and/or mechanical properties. For general discussion of polyimides preparation, characterization and applications see Polyimides, Synthesis, Characterization and Applications, K. L. Mittal, ed Plenum, N.Y. 1984.
Polyimides based on pyromellitic dianhydride (II) ##STR2## and 2,2-bis[3,5-dichloro-4-(4-aminophenyloxy)-phenyl]propane(III) ##STR3## and various copolyimides using other aromatic diamines are disclosed in U.S. Pat. No. 4,485,140 to Gannett et al (E. I. DuPont de Nemours and Co.) and preparation of two such polyimides are described in the examples.
Polyimides based on more exotic diamines such as 2,2'-di-(p-aminophenyloxy)-diphenyl (IV) ##STR4## and various dianhydrides are disclosed in U.S. Pat. No. 4,239,880 to Darms (Ciba-Geigy Corp.), and preparation of three such polyimides are described in the examples.
3,6-diphenylpyromellitic dianhydride, ##STR5## hereafter sometimes referred to as DPPMDA, has been made in poor yields by S. Liang and reported in his master's thesis: Phenylated Monomer Synthesis: trans-2,3-diphenyl-2-butenedial and 3,6-diphenyl pyromellitic dianhydride. However, neither the reported synthesis of DPPMDA or the two patents dealing with various polyimides suggest that polyimides derived from 3,6-diarylpyromellitic dianhydride will be readily soluble in certain organic solvents without loss of other important properties.
It thus appears desirable to produce polyimides based on 3,6-diarylpyromellitic dianhydride which would be soluble, have high molecular weight, high modulus, and good properties as protective coatings for microelectronics, as solution castable films, as membranes for molecular and gas separations, or as reinforcing agents in molecular composites, or as high modulus, high tensile strength fibers.